The present disclosure relates to, in various exemplary embodiments, to processes in synthesizing a branched amorphous polyester resin. The branched amorphous polyester resin of the present embodiments may be used in toners, such as Emulsion Aggregation (EA) toners, which are prepared using an emulsion aggregation process. Emulsion aggregation processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,346,797, 5,370,963, 5,344,738, 5,403,693, 5,418,108, and 5,364,729.
Toners must not aggregate or block during manufacturing, transport or storage periods before use in electrographic systems, and must exhibit low fusing temperature properties in order to minimize fuser energy requirements. Accordingly, to satisfy blocking requirements, toner resins should exhibit glass transition temperatures (Tg) of 50° C. or above (e.g., from about 40.0° C. to about 80° C.).
Fixing performance of toners can be characterized as a function of temperature and pressure. The temperature at which the toner adheres to the fuser roll is called the hot offset temperature (HOT). When the toners offsets onto the fuser roll, the image density and quality of the fused image is compromised—less dense image, incomplete image etc. At the HOT or higher, some of the molten toner adheres to the fuser roll during fixing and is transferred to subsequent substrates containing developed images, resulting for example in blurred images. This undesirable phenomenon is called offsetting. Less than the HOT of the toner is the minimum fixing temperature (MFT) of the toner, which is the minimum temperature at which acceptable adhesion of the toner to the support medium occurs. The difference between these two temperatures should be a large as possible defining an acceptable fusing temperature latitude range when toners can be fused without fusing defects. Toner resins should exhibit a MFT of 60° C. or above (e.g., from about 60° C. to about 140° C.) to adhere properly to the substrate, and a HOT of 190° C. or above (e.g., from about 190 to about 230) to avoid print defects and fuser contamination.
Pricing is another important consideration in the toner resin selection decision. Resin generally comprises more than 80% of the final toner by weight. Therefore, the price of the resin is a very large factor in the final cost to manufacture toner. Further, there are many competing technologies for the production of printed documents and graphics other than xerography. Therefore, in order to remain a technology of choice, the price of toner must be kept as low as possible.
Over time, there has been a shift toward employing low melt toner resins for improved throughput and/or reduced energy consumption. The newer generation toners incorporate so called ultra-low melt (ULM) polyester technology that includes the combination of amorphous and crystalline polyester resins to provide optimized fusing performance even in relatively simple printers. Polyesters are broadly separated into two categories of amorphous (APE) and crystalline (CPE) based on their thermal characteristics (resin flow measured by glass transition temperature or relatively sharp melting measured by the melting point). Amorphous polyesters are further broken down into linear, branched and cross-linked resins. High molecular weight branched polyesters are required in order to control fuser hot offset (i.e., residual toner build-up on the fuser roll) as well as the glossiness of the final image, which is particularly relevant for high end graphics applications. They are able to fulfill this role due to having relatively high weight average molecular weight (MW) and a relatively high degree of polydispersity which provides a substantial degree of resin elasticity. To use the polyester resins in the emulsion aggregation process, the resin must be dispersed by the phase inversion emulsification (PIE) process. This requires the resin to be completely soluble in an organic solvent prior to the addition of water and subsequent phase inversion in water.
One major difficulty in producing branched amorphous polyester resins is to properly control the degree of branching which is the fraction of the resin that is not completely soluble in solvent. The controlled amount of branching is necessary to optimize the fusing performance. In general, typical concerns with the synthesis of branched amorphous polyester resins include the uses of dangerous materials, such as, ethylene oxide and propylene oxide, which are dangerous flammable toxic gases that require special costly equipment for safe handling. Another concern with the existing process for producing branched amorphous polyesters is the isolation of the alkoxylated intermediates prior to use in the polyesterification step, which leads to additional cost and complexity in synthesizing the final branched amorphous polyester resins.
Thus, there exists a need to improve the current process of producing branched amorphous polyester resins.